The present invention relates to a method for treating a nitrogen compound of organic nitrogen, nitrite nitrogen, nitrate nitrogen, ammonia nitrogen or the like in organic waste water discharged from, e.g., a livestock breeder or the like.
It has conventionally been well known that presence of a nitrogen compound is one of causes of eutrophication of rivers and lakes. A great volume of such nitrogen compounds is present in domestic life waste water, industrial waste water or livestock breeder's waste water. At present, however, it is difficult to purify the nitrogen compounds, and no effective countermeasures are available. Especially, organic waste water (referred to as for-treatment water, hereinafter) discharged from a livestock breeder such as a hog raiser contains many organic matters of high ammonia nitrogen and organic nitrogen chemical oxygen demand (COD) or biochemical oxygen demand (BOD), and purification has been very difficult.
Aerobic biochemical treatment is generally carried out. However, since the treatment comprises two processes, i.e., a nitrification process for converting ammonia nitrogen into nitrite nitrogen, and the nitrite nitrogen into nitrate nitrogen, and a denitrification process for converting nitrate nitrogen into nitrogen gas, two reaction vessels are required, and treatment time is long, creating a problem of low treatment efficiency. Especially, since reaction efficiency of the nitrification process which oxidizes ammonia to be nitrate nitrogen is low, there has been a problem that a large reaction vessel is required.
In order to solve the above technical problems, electrolysis has conventionally been carried out to treat ammonia nitrogen, nitrite nitrogen or nitrate nitrogen in for-treatment water to nitrogen gas by using a noble metal such as platinum, iridium, or palladium for an anode, and feeding a current to the for-treatment water (e.g., Japanese Patent Application Laid-Open No. 54-16844).
However, if organic waste water discharged from the livestock breeder or the like is treated by conventional electrolysis, there is a problem of enormous power costs. Especially, much power is required for reaction to reduce nitrate nitrogen to nitrite nitrogen, and reaction to reduce nitrite nitrogen to ammonia nitrogen. Much power is also required for electrolysis of the organic matter contained in the organic waste water. Consequently, the reduction of the organic waste water containing much nitrate nitrogen to nitrogen gas only by electrolysis has a problem of a great cost burden.